1. Field of the Invention
The present invention relates to the in situ monitoring of supercritical fluid processes and, in particular, to a method and apparatus for monitoring and analyzing in real-time operating parameters in semiconductor fabrication processes employing supercritical fluids or high pressure liquids.
2. Description of Related Art
Semiconductor integrated circuits (IC's) are fabricated by a series of process steps many of which involve the use of gaseous and liquid materials. Included among such processes are etching, diffusion, chemical vapor deposition (CVD), ion implantation and the like. One important fabrication step is to clean semiconductor wafers and other IC's using a supercritical fluid or high pressure liquid and the monitoring of process conditions is important for process optimization. For example, if a co-solvent is used with the supercritical fluid/high pressure liquid, it is important to know the amount of co-solvent in the mixture during the process so that the mixture can be maintained at an optimal pre-determined concentration.
It is also important to measure the composition of the effluent to determine, among other things, the process endpoint. By monitoring both the input mixture and effluent and the composition of the supercritical fluid or high pressure liquid, the amount of co-solvent used in the process can be determined as well as numerous other operating parameters dependent upon concentration. When monitoring for endpoint verification, the effluent composition will reflect the cessation of removal of material from the workpiece or, in the case of a deposition process, the deposition material (from the co-solvent) and the effluent concentration will increase reflecting a cessation of deposition on the surface of the workpiece.
The present invention has been developed for its applicability for the semiconductor and microelectronics fabrication industries and, in particular, to the cleaning of contaminated substrates, including, for example, semiconductor wafers, multiple chip carriers, flat panel displays, magnetic hard disks and other electronic devices. Many methods have been developed to clean such surfaces and techniques include the use of solvents or chemicals, high energy sonic waves, cryogenic aerosols and combinations thereof.
The use of supercritical carbon dioxide and other supercritical fluids as well as densified liquids are now being used for cleaning semiconductor wafers. Liquid or supercritical carbon dioxide has very low surface tension, high diffusivity, solvent like properties, and no adverse environmental effects. Finally, no residual liquid remains on the precision surface, since carbon dioxide returns to its gas phase after process completion.
Unfortunately, monitoring and analyzing of supercritical fluids or high pressure liquids is very difficult, especially in situ, and such a monitoring process would have many advantages in process costs, cycle time and process repeatability.
Most conventional analysis equipment falls into the category where sampling is first effected and the sample passed to the analyzer. The analyzer normally embodies any one of the many known techniques for analysis such as photometry, spectroscopy, filter reduction and chromatography. The major disadvantage of such techniques lies in the sampling since the analyzers themselves are usually adequate whereas the sampling systems generally require a considerable amount of maintenance and are known to be unreliable.
Many processes require, or would at least benefit from, on-line monitoring of the chemical composition and/or other parameters of the reactant mixtures involved. Such in situ analysis entails a number of significant advantages over other techniques particularly in that all of the problems associated with sampling and sample handling are inherently eliminated. It also permits dynamic monitoring of chemical and/or physical changes that occur during the course of the process.
As far as is known, very few (if any) of the forms of instrumentation heretofore available are useful or satisfactory for the on-line analysis of supercritical fluid streams and high pressure liquids, as well as their mixed phases. In particular, it is not believed that any such instrumentation is capable of measuring quantitative chemical composition data for supercritical fluid and/or high pressure liquid streams, especially in a reactive environment.
Optical analyses of fluids, including gases, are well known, and various optical and spectroscopic techniques have been applied in industrial processes. In general, light is directed at the sample and the light spectrum of the reflected light (absorbance spectra) is detected and the detected spectra are fit to known spectra to obtain information regarding the composition of the tested material.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for in situ monitoring and analyzing of process fluids and/or liquids and other parameters in the fabrication of semiconductor and microelectronic components where a supercritical fluid and/or high pressure liquids are used.
It is another object of the present invention to provide an apparatus for the in situ monitoring and analyzing of process fluids and/or liquids and other parameters in the fabrication of semiconductor and microelectronic components where supercritical fluids and/or high pressure liquids are used.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.